Decrypt a mnemonic from a Krux .json file or QR code

krux_decrypt_lite.py

# The MIT License (MIT)

# Copyright (c) 2021-2023 Krux contributors

# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:

# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.

# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
# THE SOFTWARE.

# Python requirements: pycryptodome, opencv-python, pyzbar, embit
#  pip install pycryptodome opencv-python pyzbar embit
# OS may require: zbar-tools (sudo apt install zbar-tools)

# Usage:

# Decrypt a mnemonic from a json file:
#  python krux_decrypt.py json --file seeds.json

# Scan and decrypt an encrypted mnemonic QR code:
#  python krux_decrypt.py qr

import time
import hashlib
import base64
import argparse
import json
from Crypto.Cipher import AES
import cv2
from pyzbar.pyzbar import decode
from embit import bip39


PBKDF2_HMAC_ECB = 0
PBKDF2_HMAC_CBC = 1
AES_BLOCK_SIZE = 16

VERSION_MODE = {
    "AES-ECB": AES.MODE_ECB,
    "AES-CBC": AES.MODE_CBC,
    PBKDF2_HMAC_ECB: AES.MODE_ECB,
    PBKDF2_HMAC_CBC: AES.MODE_CBC,
}

VERSION_NUMBER = {
    "AES-ECB": PBKDF2_HMAC_ECB,
    "AES-CBC": PBKDF2_HMAC_CBC,
}


class AESCipher(object):
    """Helper for AES encrypt/decrypt"""

    def __init__(self, key, salt, iterations):
        self.key = hashlib.pbkdf2_hmac(
            "sha256", key.encode(), salt.encode(), iterations
        )

    def decrypt(self, encrypted, mode, iv=None):
        """Decrypt a base64 using AES MODE_ECB and return the value decoded as string"""
        if iv:
            decryptor = AES.new(self.key, mode, iv)
        else:
            decryptor = AES.new(self.key, mode)
        load = decryptor.decrypt(encrypted).decode("utf-8")
        return load.replace("\x00", "")

    def decrypt_bytes(self, encrypted, mode, i_vector=None):
        """Decrypt and return value as bytes"""
        if i_vector:
            decryptor = AES.new(self.key, mode, i_vector)
        else:
            decryptor = AES.new(self.key, mode)
        return decryptor.decrypt(encrypted)


class MnemonicStorage:
    """Handler of stored encrypted seeds"""

    def __init__(self, json_vault) -> None:
        self.stored = json_vault

    def list_mnemonics(self, sd_card=False):
        """List all seeds stored on a file"""
        mnemonic_ids = []
        for mnemonic_id in self.stored:
            mnemonic_ids.append(mnemonic_id)
        return mnemonic_ids

    def decrypt(self, key, mnemonic_id):
        """Decrypt a selected encrypted mnemonic from a file"""
        try:
            encrypted_data = self.stored.get(mnemonic_id)["data"]
            iterations = self.stored.get(mnemonic_id)["key_iterations"]
            version = self.stored.get(mnemonic_id)["version"]
        except:
            return None
        data = base64.b64decode(encrypted_data)
        mode = VERSION_MODE[version]
        if mode == AES.MODE_ECB:
            encrypted_mnemonic = data
            iv = None
        else:
            encrypted_mnemonic = data[AES_BLOCK_SIZE:]
            iv = data[:AES_BLOCK_SIZE]
        decryptor = AESCipher(key, mnemonic_id, iterations)
        words = decryptor.decrypt(encrypted_mnemonic, mode, iv)
        return words


class EncryptedQRCode:
    """Creates and decrypts encrypted mnemonic QR codes"""

    def __init__(self) -> None:
        self.mnemonic_id = None
        self.version = None
        self.iterations = None
        self.encrypted_data = None

    def public_data(self, data):
        """Parse and returns encrypted mnemonic QR codes public data"""
        mnemonic_info = "Encrypted QR Code:\n"
        try:
            id_length = int.from_bytes(data[:1], "big")
            self.mnemonic_id = data[1 : id_length + 1].decode("utf-8")
            mnemonic_info += "ID: " + self.mnemonic_id + "\n"
            self.version = int.from_bytes(data[id_length + 1 : id_length + 2], "big")
            version_name = [k for k, v in VERSION_NUMBER.items() if v == self.version][
                0
            ]
            mnemonic_info += "Version: " + version_name + "\n"
            self.iterations = int.from_bytes(data[id_length + 2 : id_length + 5], "big")
            self.iterations *= 10000
            mnemonic_info += "Key iter.: " + str(self.iterations)
        except:
            return None
        extra_bytes = id_length + 5  # 1(id length byte) + 1(version) + 3(iterations)
        if self.version == 1:
            extra_bytes += 16  # Initial Vector size
        extra_bytes += 16  # Encrypted QR checksum is always 16 bytes
        len_mnemonic_bytes = len(data) - extra_bytes
        if len_mnemonic_bytes not in (16, 32):
            print(len_mnemonic_bytes)
            return None
        self.encrypted_data = data[id_length + 5 :]
        return mnemonic_info

    def decrypt(self, key):
        """Decrypts encrypted mnemonic QR codes"""
        mode = VERSION_MODE[self.version]
        if mode == AES.MODE_ECB:
            encrypted_mnemonic_data = self.encrypted_data
            i_vector = None
        else:
            encrypted_mnemonic_data = self.encrypted_data[AES_BLOCK_SIZE:]
            i_vector = self.encrypted_data[:AES_BLOCK_SIZE]
        success = False
        decryptor = AESCipher(key, self.mnemonic_id, self.iterations)
        decrypted_data = decryptor.decrypt_bytes(
            encrypted_mnemonic_data, mode, i_vector
        )
        mnemonic_data = decrypted_data[:-AES_BLOCK_SIZE]
        checksum = decrypted_data[-AES_BLOCK_SIZE:]
        # Data validation:
        if hashlib.sha256(mnemonic_data).digest()[:16] == checksum:
            success = True

        return mnemonic_data if success else None


def scan():
    """Opens a scan window and uses cv2 to detect and decode a QR code, returning its data"""
    vid = cv2.VideoCapture(0)
    qr_data = None
    while True:
        # Capture the video frame by frame
        _, frame = vid.read()
        try:
            qr_data = decode(frame)
        except:
            qr_data = []
        # _, _, _ = detector.detectAndDecode(frame)
        if qr_data:
            break
        # Display the resulting frame
        cv2.imshow("frame", frame)
        if cv2.waitKey(1) & 0xFF == ord("q"):
            break
    vid.release()
    cv2.destroyAllWindows()
    return qr_data[0].data


parser = argparse.ArgumentParser(
    prog="krux_decrypt",
    description="Python script to decrypt Krux encrypted mnemonics",
)

subparsers = parser.add_subparsers(help="sub-command help", dest="command")
qr_parser = subparsers.add_parser("qr", help="scans an decrypt an encrypted QR code")

file_parser = subparsers.add_parser(
    "json", help="loads and decrypt a mnemonic from a Krux encrypted .json file"
)
file_parser.add_argument("--file", dest="json_file", help="path to file to .json file")


args = parser.parse_args()
if args.command == "qr":
    _ = input("Press enter to scan an encrypted mnemonic")
    scanned_data = scan()
    encrypted_qr = EncryptedQRCode()
    print(encrypted_qr.public_data(scanned_data.decode().encode("latin-1")))
    typed_key = input("Enter decryption key: ")

    binary_mnemonic = encrypted_qr.decrypt(typed_key)
    if binary_mnemonic:
        print(bip39.mnemonic_from_bytes(binary_mnemonic))
    else:
        print("Failed to decrypt")
elif args.command == "json":
    if args.json_file is None:
        print("Please specify a file")
    else:
        json_file = open(args.json_file, "r")
        json_vault = json.loads(json_file.read())
        json_file.close()
        vault = MnemonicStorage(json_vault)
        print("Stored Mnemonics:")
        stored_mnemonics = vault.list_mnemonics()
        for i, mnemonic in enumerate(stored_mnemonics):
            print(str(i) + ":", mnemonic)
        valid_index = False
        while not valid_index:
            try:
                mnemonic_index = int(
                    input("Enter the index of the mnemonic you wish to decrypt: ")
                )
                valid_index = True
            except:
                print("Please enter a integer number")
        typed_key = input("Enter decryption key: ")
        binary_mnemonic = vault.decrypt(typed_key, stored_mnemonics[mnemonic_index])
        print(binary_mnemonic)


else:
    parser.print_help()